Mark com.zaxxer:HikraiCP as an intentionally unused dependency

Boot has upgraded to HikariCP 2.1 where the HikariCP artifact
requires Java 8. As a result, Boot now depends upon HikariCP-java6.
Dependency management for HikariCP has been retained to provide better
backwards compatibility and to support those who are not yet running
on Java 8.
Merge branch '1.1.x'